Defective CYP7B1 causes SPG5A and CBAS3

Bile acids are synthesised from cholesterol via two pathways - a classic neutral pathway involving cholesterol 7-alpha-hydroxylase (CYP7A1), and an acidic pathway involving 25-hydroxycholesterol 7-alpha-hydroxylase (CYP7B1). Defects in CYP7B1 can cause spastic paraplegia 5A (SPG5A), a neurodegenerative disorder characterised by a slow, gradual, progressive weakness and spasticity of the lower limbs. Defects in CYP7B1 can also cause Congenital bile acid synthesis defect 3 (CBAS3; MIM:613812), a disorder resulting in severe cholestasis, cirrhosis and liver synthetic failure. Hepatic CYP7B1 activity is undetectable.

Summary from Reactome (R-HSA-5579013), read 2026-09-23.